FM 23-81 37-mm Gun Tank M6 (Mounted in Tanks) 1942-04-02
"The 37-mm tank gun M6 is a flat trajectory weapon of the field gun type similar to the M5 gun described in FM 23-80. It fires projectiles which weigh about 2 pounds. The main features distinguishing the M6 gun from the M5 is that it has a longer barrel, the breechblock is operated automatically, and the mount is provided with a breech operating mechanism."
Digitized by AHEC (U.S. Army Heritage Collections) http://www.carlisle.army.mil/ahec/
"April 3, 1942"--Cover
"This manual supersedes so much of section I, Training circular no. 39, War Department, 1941, as pertains to FM 23-81"--Page 1